Anything the makes the game harder is appreciated and if most players have to drop a difficulty level I would call that success.
To achieve this result, cities have to be so vulnerable that it is dangerous to leave room for 5ish units to attack the city..
This is a question for me, would reduce city attacks make the AI stronger or weaker?
On the one hand, the AI is terrible at combat. If battles happen more at in the field, the human is going to win them...and the city won't be able to compensate.
On the other hand, the AI has more units, and its common for a smart human to use their city to weaken down the hoards as their armies do what needs doing. If that tactic is weaker, it might strength the AI horde tactics.
Ultimately I am not sure.